diff --git a/static/apidocs/openapi.yml b/static/apidocs/openapi.yml
index 2b0226f..6aef7bc 100644
--- a/static/apidocs/openapi.yml
+++ b/static/apidocs/openapi.yml
@@ -23,6 +23,7 @@ info:
     * **Breaking change:** POST `/spot` now expects `activities` (a list) and `activity_refs` in the `spot` object, rather than `sig` and `sig_refs`.
     * **Breaking change:** In the `/options` response, `sigs` has been renamed to `activities`, and within each activity, `sig_type` has been renamed to `activity_type`.
     * **Breaking change:** In the `/status` response, `sig_ref_data_providers` has been renamed to `activity_ref_data_providers`, and within each provider, `sig_name` has been renamed to `activity_name`.
+    * **Breaking change:** In the POST `/spot` `handling` object, `submit_upstream` and `upstream_provider` have been replaced by `upstream_providers`, a list of provider names, so a spot can be sent to multiple upstream providers at once. `upstream_credentials` is now a map of provider name to that provider's credentials.
     
     #### Upgrading a client from v2 to v3 API endpoints
 
@@ -940,6 +941,7 @@ components:
         - BIWOTA
         - COTA
         - PGA
+        - Railways
         - Toilets
       example: POTA
 
@@ -1381,30 +1383,30 @@ components:
           description: >
             Optional server-side instructions for how to process this spot submission.
           properties:
-            submit_upstream:
-              type: boolean
+            upstream_providers:
+              type: array
+              items:
+                type: string
               description: >
-                If true, forward the spot to an external upstream provider (e.g. POTA, SOTA) rather than only adding it
-                to this Spothole server. Requires `upstream_provider` to be set. Check `spot_submit_providers` in the
-                `/options` response to see which activities and providers support this.
-              default: false
-            upstream_provider:
-              type: string
-              description: >
-                Name of the upstream provider to submit the spot to, e.g. "POTA" or "SOTA". Must
-                match one of the provider names returned in `spot_submit_providers` for the chosen activity.
-              example: POTA
+                Names of upstream providers to forward the spot to (e.g. "POTA", "SOTA"), in addition to or instead
+                of only adding it to this Spothole server. Each name must match one of the provider names returned in
+                `spot_submit_providers` in the `/options` response for the chosen activity. Omit or leave empty to
+                add the spot to this Spothole server only.
+              example: [ POTA, ParksNPeaks ]
             upstream_credentials:
               type: object
               description: >
-                Provider-specific credentials required to authenticate the upstream submission.
-                The required keys depend on the provider. Credentials are used only for the upstream
-                call and are never stored by Spothole.
+                A map of provider name to the provider-specific credentials required to authenticate the upstream
+                submission to that provider. The required keys depend on the provider. Credentials are used only for
+                the upstream call and are never stored by Spothole.
               additionalProperties:
-                type: string
+                type: object
+                additionalProperties:
+                  type: string
               example:
-                user_id: "12345"
-                api_key: "abc123"
+                ParksNPeaks:
+                  user_id: "12345"
+                  api_key: "abc123"
             captcha_token:
               type: string
               description: >
@@ -2294,9 +2296,9 @@ components:
           type: object
           description: >
             A map of activity name to a list of provider names that support upstream spot submission for that
-            activity. If an activity appears as a key here, the POST /spot endpoint accepts `submit_upstream: true`
-            for spots with that activity, and will forward the spot to one of the listed providers. Omitted if no
-            providers support upstream submission.
+            activity. If an activity appears as a key here, the POST /spot endpoint accepts these provider names in
+            `upstream_providers` for spots with that activity, and will forward the spot to any of the listed
+            providers. Omitted if no providers support upstream submission.
           additionalProperties:
             type: array
             items:
diff --git a/static/js/add-spot.js b/static/js/add-spot.js
index 9c187f4..f553b44 100644
--- a/static/js/add-spot.js
+++ b/static/js/add-spot.js
@@ -63,46 +63,46 @@ function updateUpstreamArea() {
 
     $("#upstream-area").show();
 
-    // Update the provider selector
-    $("#upstream-provider-select").empty();
+    // Rebuild the provider checkboxes, keeping any that were already checked for the previous activity
+    const previouslyChecked = getSelectedUpstreamProviders();
+    const container = $("#upstream-providers").empty();
     $.each(providers, function (i, name) {
-        $("#upstream-provider-select").append($('<option>', {value: name, text: name}));
+        const id = "submit-upstream-" + i;
+        const row = $("<div class='row g-2 align-items-center mb-1'></div>");
+        const check = $("<div class='form-check'></div>");
+        check.append($("<input class='form-check-input upstream-provider-check' type='checkbox'>")
+            .attr("id", id).val(name).prop("checked", previouslyChecked.includes(name)));
+        check.append($("<label class='form-check-label'></label>").attr("for", id).text(name));
+        row.append($("<div class='col-auto'></div>").append(check));
+
+        // Add a credentials button if this provider has an authentication mechanism and we need input from the user
+        if (PROVIDER_CREDENTIAL_SCHEMAS[name]) {
+            const button = $("<button type='button' class='btn btn-sm btn-outline-secondary'></button>")
+                .attr("aria-label", "Credentials for " + name)
+                .html("<i class='fa-solid fa-key'></i> Credentials")
+                .click(() => showCredentialsModal(name));
+            row.append($("<div class='col-auto'></div>").append(button));
+        }
+        container.append(row);
     });
-
-    if (providers.length > 1) {
-        $("#upstream-provider-label").text("upstream spot sources:");
-        $("#upstream-provider-select-col").show();
-    } else {
-        $("#upstream-provider-label").text(providers[0]);
-        $("#upstream-provider-select-col").hide();
-    }
-
-    // Show the credentials button if this provider has an authentication mechanism and we need input from the user
-    updateCredentialsButton();
+    updateSpotholeOnlyCheck();
 }
 
-// Update the credentials button visibility based on selected provider
-function updateCredentialsButton() {
-    const providerName = getSelectedUpstreamProvider();
-    if (providerName && PROVIDER_CREDENTIAL_SCHEMAS[providerName]) {
-        $("#upstream-credentials-btn").show();
-    } else {
-        $("#upstream-credentials-btn").hide();
-    }
+// The "Spothole only" checkbox is checked when no upstream providers are selected
+function updateSpotholeOnlyCheck() {
+    $("#spothole-only").prop("checked", getSelectedUpstreamProviders().length === 0);
 }
 
-// Get the currently selected upstream provider name
-function getSelectedUpstreamProvider() {
-    const providers = SPOT_SUBMIT_PROVIDERS[$("#activity").val()] || [];
-    if (providers.length === 0) return null;
-    if (providers.length === 1) return providers[0];
-    return $("#upstream-provider-select").val();
+// Get the names of the upstream providers the user has chosen to send the spot to
+function getSelectedUpstreamProviders() {
+    return $(".upstream-provider-check:checked").map(function () {
+        return $(this).val();
+    }).get();
 }
 
-// Show the credentials modal for the currently selected upstream provider
-function showCredentialsModal() {
-    const providerName = getSelectedUpstreamProvider();
-    if (!providerName || !PROVIDER_CREDENTIAL_SCHEMAS[providerName]) return;
+// Show the credentials modal for the given upstream provider
+function showCredentialsModal(providerName) {
+    if (!PROVIDER_CREDENTIAL_SCHEMAS[providerName]) return;
 
     const schema = PROVIDER_CREDENTIAL_SCHEMAS[providerName];
     const stored = loadCredentials(providerName);
@@ -187,12 +187,13 @@ function addSpot() {
         }
 
         // Upstream submission
-        const submitUpstream = $("#submit-upstream").is(":checked");
-        const upstreamProviderName = getSelectedUpstreamProvider();
-        if (submitUpstream && upstreamProviderName) {
-            handling["submit_upstream"] = true;
-            handling["upstream_provider"] = upstreamProviderName;
-            handling["upstream_credentials"] = loadCredentials(upstreamProviderName);
+        const upstreamProviders = getSelectedUpstreamProviders();
+        if (upstreamProviders.length > 0) {
+            handling["upstream_providers"] = upstreamProviders;
+            handling["upstream_credentials"] = {};
+            $.each(upstreamProviders, function (i, name) {
+                handling["upstream_credentials"][name] = loadCredentials(name);
+            });
         }
 
         $.ajax("/api/v3/spot", {
@@ -262,14 +263,21 @@ $("#mode").change(function () {
     $(this).val($(this).val().trim().toUpperCase());
 });
 
-// Update upstream area and credentials button when activity changes
+// Update upstream area when activity changes
 $("#activity").change(function () {
     updateUpstreamArea();
 });
 
-// Update credentials button when provider selector changes
-$("#upstream-provider-select").change(function () {
-    updateCredentialsButton();
+// Keep the "Spothole only" checkbox in sync with the upstream provider checkboxes
+$("#upstream-providers").on("change", ".upstream-provider-check", function () {
+    updateSpotholeOnlyCheck();
+});
+
+// Clicking "Spothole only" deselects all upstream providers. It can't be unchecked directly, as that would leave
+// nowhere to send the spot; the user unchecks it implicitly by choosing an upstream provider instead.
+$("#spothole-only").change(function () {
+    $(".upstream-provider-check").prop("checked", false);
+    updateSpotholeOnlyCheck();
 });
 
 // Startup
diff --git a/templates/add-spot.html b/templates/add-spot.html
index 86cfd29..35b8031 100644
--- a/templates/add-spot.html
+++ b/templates/add-spot.html
@@ -71,6 +71,16 @@
                     <input type="text" class="form-control storeable-text input-narrow" id="de-call"
                            placeholder="N0CALL" required>
                 </div>
+
+                <div id="upstream-area" class="mt-3" style="display:none;">
+                    <div class="form-label">Spot to:</div>
+                    <div class="form-check mb-1">
+                        <input class="form-check-input" type="checkbox" id="spothole-only" checked>
+                        <label class="form-check-label" for="spothole-only">Spothole only</label>
+                    </div>
+                    <div id="upstream-providers"></div>
+                </div>
+
                 <div class="col-auto">
                     <button type="submit" id="add-spot-submit" class="btn btn-primary mt-2em">
                         <span id="add-spot-spinner" class="spinner-border spinner-border-sm me-1" aria-hidden="true"
@@ -80,28 +90,6 @@
                 </div>
             </form>
 
-            <div id="upstream-area" class="mt-3" style="display:none;">
-                <div class="row g-2 align-items-center">
-                    <div class="col-auto">
-                        <div class="form-check">
-                            <input class="form-check-input" type="checkbox" id="submit-upstream">
-                            <label class="form-check-label" for="submit-upstream">
-                                Send spot to <span id="upstream-provider-label"></span>
-                            </label>
-                        </div>
-                    </div>
-                    <div class="col-auto" id="upstream-provider-select-col" style="display:none;">
-                        <select id="upstream-provider-select" class="form-select form-select-sm"></select>
-                    </div>
-                    <div class="col-auto">
-                        <button type="button" class="btn btn-sm btn-outline-secondary" id="upstream-credentials-btn"
-                                onclick="showCredentialsModal();" style="display:none;">
-                            <i class="fa-solid fa-key"></i> Credentials
-                        </button>
-                    </div>
-                </div>
-            </div>
-
             <div id="recaptcha-area" class="mt-3" style="display:none;">
                 <div id="recaptcha-widget"></div>
             </div>
@@ -142,7 +130,7 @@
     const ALLOW_UPSTREAM_SPOTTING = {% raw safe_json_dumps(web_ui_options["allow_upstream_spotting"]) %};
 </script>
 
-<script src="/static/js/add-spot.js?v=1790514703"></script>
+<script src="/static/js/add-spot.js?v=1790516268"></script>
 <script>$(document).ready(function () {
     $("#nav-link-add-spot").addClass("active");
 }); <!-- highlight active page in nav --></script>
diff --git a/templates/alerts.html b/templates/alerts.html
index d52182c..8616a2c 100644
--- a/templates/alerts.html
+++ b/templates/alerts.html
@@ -87,7 +87,7 @@
 
 </div>
 
-<script src="/static/js/alerts.js?v=1790514703"></script>
+<script src="/static/js/alerts.js?v=1790516268"></script>
 <script>$(document).ready(function () {
     $("#nav-link-alerts").addClass("active");
 }); <!-- highlight active page in nav --></script>
diff --git a/templates/bands.html b/templates/bands.html
index 2e8a449..1a63844 100644
--- a/templates/bands.html
+++ b/templates/bands.html
@@ -82,8 +82,8 @@
     const BANDS = {% raw safe_json_dumps(options["bands"]) %};
 </script>
 
-<script src="/static/js/spotsbandsandmap.js?v=1790514703"></script>
-<script src="/static/js/bands.js?v=1790514703"></script>
+<script src="/static/js/spotsbandsandmap.js?v=1790516268"></script>
+<script src="/static/js/bands.js?v=1790516268"></script>
 <script>$(document).ready(function () {
     $("#nav-link-bands").addClass("active");
 }); <!-- highlight active page in nav --></script>
diff --git a/templates/base.html b/templates/base.html
index 74f17e9..cc1b96d 100644
--- a/templates/base.html
+++ b/templates/base.html
@@ -1,6 +1,6 @@
 {% extends "skeleton.html" %}
 {% block head_extra %}
-<link rel="stylesheet" href="/static/css/style.css?v=1790514702" type="text/css">
+<link rel="stylesheet" href="/static/css/style.css?v=1790516268" type="text/css">
 <link href="/static/vendor/css/bootstrap-5.3.8.min.css" rel="stylesheet">
 <link href="/static/vendor/css/fontawesome-6.7.2.min.css" rel="stylesheet">
 <link href="/static/vendor/css/solid-6.7.2.min.css" rel="stylesheet">
@@ -16,10 +16,10 @@
     window.fetchEventSource = fetchEventSource;
 </script>
 
-<script src="/static/js/utils.js?v=1790514702"></script>
-<script src="/static/js/ui-ham.js?v=1790514702"></script>
-<script src="/static/js/geo.js?v=1790514702"></script>
-<script src="/static/js/common.js?v=1790514702"></script>
+<script src="/static/js/utils.js?v=1790516268"></script>
+<script src="/static/js/ui-ham.js?v=1790516268"></script>
+<script src="/static/js/geo.js?v=1790516268"></script>
+<script src="/static/js/common.js?v=1790516268"></script>
 {% end %}
 {% block body %}
 <div class="container">
diff --git a/templates/conditions.html b/templates/conditions.html
index 46c4729..a5f2b9d 100644
--- a/templates/conditions.html
+++ b/templates/conditions.html
@@ -284,7 +284,7 @@
 </div>
 
 <script src="/static/vendor/js/chart-4.4.9.umd.min.js"></script>
-<script src="/static/js/conditions.js?v=1790514702"></script>
+<script src="/static/js/conditions.js?v=1790516268"></script>
 <script>$(document).ready(function () {
     $("#nav-link-conditions").addClass("active");
 }); <!-- highlight active page in nav --></script>
diff --git a/templates/help/thanks.html b/templates/help/thanks.html
index 5ce9437..069d2f7 100644
--- a/templates/help/thanks.html
+++ b/templates/help/thanks.html
@@ -9,11 +9,12 @@
         modelling software, and other online tools on which Spothole's data is based. The vast majority of these are not
         profit-seeking and are made purely for the love of the hobby and to help others in the community. Spothole is
         standing on the shoulders of giants, who deserve a huge amount of thanks for all the work they put in.</p>
-    <p>The following people have specifically helped develop Spothole either by contributing code, requesting features,
-    or helping squash bugs: Steven M1SDH, Dan S50U, Matt W1CDN, Norby LX1NO, Andrew VK3ARR, Mario DL4MFM, Mark M5TEA,
-        Michael G7VJR, Rob G7LAS, Ed DD5LP, Raph F4LUB, Luc ON7KEC, Richard GD4OFB, Daniel PY2TDB, Alan VK1AO,
-        Andrew WK1AD, Ullrich DF5WC, Wayne N3CDF, Jonathan G4IVV, Erik N2EPE, Sorin YO9TSN, Matt HB9HWI, Priit ES1TEB,
-        Leigh KG7WED, Jouni OH3CUF, Onno VK6FLAB, and Bruce WA7BNM. (If I've forgotten you, let me know!)</p>
+    <p>The following people have specifically helped develop Spothole either by contributing code, allowing access to
+        their data, providing guidance, requesting features, or helping squash bugs: Steven M1SDH, Dan S50U, Matt W1CDN,
+        Norby LX1NO, Andrew VK3ARR, Mario DL4MFM, Mark M5TEA, Michael G7VJR, Rob G7LAS, Ed DD5LP, Raph F4LUB,
+        Luc ON7KEC, Richard GD4OFB, Daniel PY2TDB, Alan VK1AO, Andrew WK1AD, Ullrich DF5WC, Wayne N3CDF, Jonathan G4IVV,
+        Erik N2EPE, Sorin YO9TSN, Matt HB9HWI, Priit ES1TEB, Leigh KG7WED, Jouni OH3CUF, Onno VK6FLAB, Bruce WA7BNM, and
+        Larry F5PYI. (If I've forgotten you, let me know!)</p>
     <p>Spothole is also dependent on a number of Python libraries, such as pyhamtools, and many JavaScript
         libraries, as well as the Font Awesome icon set and flag icons from the Noto Color Emoji set, and MIT-licenced
         GeoJSON files for CQ and ITU zones from HA8TKS.</p>
diff --git a/templates/map.html b/templates/map.html
index 922714e..e1adf27 100644
--- a/templates/map.html
+++ b/templates/map.html
@@ -115,8 +115,8 @@
     const CARTODB_API_KEY = "{{ web_ui_options.get('cartodb_api_key', '') }}";
 </script>
 
-<script src="/static/js/spotsbandsandmap.js?v=1790514702"></script>
-<script src="/static/js/map.js?v=1790514702"></script>
+<script src="/static/js/spotsbandsandmap.js?v=1790516267"></script>
+<script src="/static/js/map.js?v=1790516267"></script>
 <script>$(document).ready(function () {
     $("#nav-link-map").addClass("active");
 }); <!-- highlight active page in nav --></script>
diff --git a/templates/spots.html b/templates/spots.html
index 2fa23b2..95ea600 100644
--- a/templates/spots.html
+++ b/templates/spots.html
@@ -127,8 +127,8 @@
 
 </div>
 
-<script src="/static/js/spotsbandsandmap.js?v=1790514702"></script>
-<script src="/static/js/spots.js?v=1790514702"></script>
+<script src="/static/js/spotsbandsandmap.js?v=1790516267"></script>
+<script src="/static/js/spots.js?v=1790516267"></script>
 <script>$(document).ready(function () {
     $("#nav-link-spots").addClass("active");
 }); <!-- highlight active page in nav --></script>
diff --git a/templates/status.html b/templates/status.html
index 51acc50..005f30d 100644
--- a/templates/status.html
+++ b/templates/status.html
@@ -96,7 +96,7 @@
     </div>
 </div>
 
-<script src="/static/js/status.js?v=1790514703"></script>
+<script src="/static/js/status.js?v=1790516268"></script>
 <script>
     $(document).ready(function () {
         $("#nav-link-status").addClass("active");
diff --git a/webserver/handlers/api/addspot.py b/webserver/handlers/api/addspot.py
index 4317a60..1bc1580 100644
--- a/webserver/handlers/api/addspot.py
+++ b/webserver/handlers/api/addspot.py
@@ -1,3 +1,4 @@
+import asyncio
 import logging
 import re
 import threading
@@ -78,9 +79,9 @@ class APISpotHandler(tornado.web.RequestHandler):
             handling = json_body.get("handling", {})
 
             # Extract individual parameters that say how this spot should be handled by the server
-            submit_upstream = handling.get("submit_upstream", False)
-            upstream_provider_name = handling.get("upstream_provider", None)
-            upstream_credentials = handling.get("upstream_credentials", {})
+            upstream_provider_names = handling.get("upstream_providers", None) or []
+            upstream_credentials = handling.get("upstream_credentials", None) or {}
+            submit_upstream = len(upstream_provider_names) > 0
             captcha_token = handling.get("captcha_token", None)
 
             # Verify CAPTCHA if required
@@ -166,13 +167,18 @@ class APISpotHandler(tornado.web.RequestHandler):
                 self.set_header("Content-Type", "application/json")
                 return
 
-            # Validate upstream submission requirements
-            if submit_upstream and upstream_provider_name:
-                is_cluster = isinstance(self._find_provider(upstream_provider_name, spot.activities), DXCluster)
-                is_tiles = isinstance(self._find_provider(upstream_provider_name, spot.activities), Tiles)
+            # Validate upstream submission requirements for each requested provider
+            for upstream_provider_name in upstream_provider_names:
+                provider = self._find_provider(upstream_provider_name, spot.activities)
+                is_cluster = isinstance(provider, DXCluster)
+                is_tiles = isinstance(provider, Tiles)
                 if not spot.activity_refs and not is_tiles and not is_cluster:
                     self.set_status(422)
-                    self.write(safe_json_dumps("Error - an activity reference is required to submit upstream."))
+                    self.write(
+                        safe_json_dumps(
+                            f"Error - an activity reference is required to submit upstream to {upstream_provider_name}."
+                        )
+                    )
                     self.set_header("Cache-Control", "no-store")
                     self.set_header("Content-Type", "application/json")
                     return
@@ -191,46 +197,27 @@ class APISpotHandler(tornado.web.RequestHandler):
                     self.set_header("Content-Type", "application/json")
                     return
 
-            # Submit upstream if requested
-            upstream_warning = None
-            if submit_upstream and upstream_provider_name:
-                provider = self._find_provider(upstream_provider_name, spot.activities)
-                if provider:
-                    try:
-                        # Submit spot to the upstream provider. Run in a separate thread otherwise this blocks the whole
-                        # web server for everyone!
-                        await IOLoop.current().run_in_executor(None, provider.submit_spot, spot, upstream_credentials)
-                        # Trigger a re-poll after 3 second so the spot appears quickly. (Submitting to a cluster node is
-                        # slower than this, but we get data as a live stream from cluster anyway, so force_poll does
-                        # nothing in that case. This is really just for the HTTP providers when we submit a spot to them)
-                        threading.Timer(3.0, provider.force_poll).start()
-                    except NotImplementedError as e:
-                        upstream_warning = str(e)
-                    except SpotSubmissionError as e:
-                        logger.warning(f"Upstream submission to {upstream_provider_name} was not accepted: {e}")
-                        upstream_warning = (
-                            f"Spot was saved locally but upstream submission to {upstream_provider_name} failed: {e}"
-                        )
-                    except Exception:
-                        logger.exception(f"Failed to submit spot upstream to {upstream_provider_name}")
-                        upstream_warning = (
-                            f"Spot was saved locally but upstream submission to {upstream_provider_name} failed."
-                        )
-                elif spot.activities:
-                    upstream_warning = f"No enabled provider named '{upstream_provider_name}' supports upstream submission for {', '.join(spot.activities)} spots."
-                else:
-                    upstream_warning = f"No enabled provider named '{upstream_provider_name}' supports upstream submission for spots with no activity."
+            # Submit upstream to all requested providers in parallel, collecting any warnings
+            results = await asyncio.gather(
+                *(
+                    self._submit_upstream(name, spot, upstream_credentials.get(name, {}))
+                    for name in upstream_provider_names
+                )
+            )
+            upstream_warnings = [w for w in results if w]
+            any_upstream_succeeded = len(upstream_warnings) < len(upstream_provider_names)
 
-            # If we successfully submitted the spot upstream, don't add it direct to Spothole, otherwise it will be a
-            # duplicate with what immediately comes back from the API. But if we weren't asked to send it upstream, or
-            # we were but it failed, we should still add it to our database anyway.
-            if not submit_upstream or upstream_warning:
+            # If we successfully submitted the spot to at least one upstream provider, don't add it direct to Spothole,
+            # otherwise it will be a duplicate with what immediately comes back from the API. But if we weren't asked to
+            # send it upstream, or we were but every submission failed, we should still add it to our database anyway.
+            if not any_upstream_succeeded:
                 spot.source = "API"
                 spot.infer_missing()
                 self._spots.set(spot.id, spot)
 
-            if upstream_warning:
-                self.write(safe_json_dumps(f"Warning - {upstream_warning}"))
+            if upstream_warnings:
+                saved_locally_note = "" if any_upstream_succeeded else " The spot was saved to Spothole only."
+                self.write(safe_json_dumps(f"Warning - {' '.join(upstream_warnings)}{saved_locally_note}"))
                 self.set_status(201)
             else:
                 self.write(safe_json_dumps("OK"))
@@ -245,6 +232,33 @@ class APISpotHandler(tornado.web.RequestHandler):
             self.set_header("Cache-Control", "no-store")
             self.set_header("Content-Type", "application/json")
 
+    async def _submit_upstream(self, upstream_provider_name, spot, credentials) -> str | None:
+        """Submit a spot to the named upstream provider. Returns None on success, or a warning message on failure."""
+
+        provider = self._find_provider(upstream_provider_name, spot.activities)
+        if not provider:
+            if spot.activities:
+                return f"No enabled provider named '{upstream_provider_name}' supports upstream submission for {', '.join(spot.activities)} spots."
+            return f"No enabled provider named '{upstream_provider_name}' supports upstream submission for spots with no activity."
+
+        try:
+            # Submit spot to the upstream provider. Run in a separate thread otherwise this blocks the whole web server
+            # for everyone!
+            await IOLoop.current().run_in_executor(None, provider.submit_spot, spot, credentials)
+            # Trigger a re-poll after 3 second so the spot appears quickly. (Submitting to a cluster node is slower than
+            # this, but we get data as a live stream from cluster anyway, so force_poll does nothing in that case. This
+            # is really just for the HTTP providers when we submit a spot to them)
+            threading.Timer(3.0, provider.force_poll).start()
+            return None
+        except NotImplementedError as e:
+            return str(e)
+        except SpotSubmissionError as e:
+            logger.warning(f"Upstream submission to {upstream_provider_name} was not accepted: {e}")
+            return f"Upstream submission to {upstream_provider_name} failed: {e}"
+        except Exception:
+            logger.exception(f"Failed to submit spot upstream to {upstream_provider_name}")
+            return f"Upstream submission to {upstream_provider_name} failed."
+
     def _find_provider(self, provider_name, activities) -> SpotProvider | None:
         """Find an enabled provider by name that can submit spots for at least one of the given activities. If there
         are no activities, find one that can submit spots with no activity."""
diff --git a/webserver/handlers/api/compatibility/v2_compatibility.py b/webserver/handlers/api/compatibility/v2_compatibility.py
index c4800f0..8b88c9e 100644
--- a/webserver/handlers/api/compatibility/v2_compatibility.py
+++ b/webserver/handlers/api/compatibility/v2_compatibility.py
@@ -116,6 +116,8 @@ class V2APISpotHandler(V2CompatibilityWrapper, RequestCompatibilityWrapper, APIS
         def translate(body):
             if isinstance(body, dict) and isinstance(body.get("spot"), dict):
                 body["spot"] = self._translate_v2_spot(body["spot"])
+            if isinstance(body, dict) and isinstance(body.get("handling"), dict):
+                body["handling"] = self._translate_v2_handling(body["handling"])
             return body
 
         translate_json_body(self.request, translate)
@@ -141,6 +143,21 @@ class V2APISpotHandler(V2CompatibilityWrapper, RequestCompatibilityWrapper, APIS
             spot_data["activity_refs"] = refs
         return spot_data
 
+    @staticmethod
+    def _translate_v2_handling(handling):
+        """Translate the "handling" object provided by a client calling the add spot method in v2 format into v3
+        format. v2 had a "submit_upstream" flag with a single "upstream_provider" and its credentials, whereas v3 has
+        a list of "upstream_providers" and a map of provider name to credentials."""
+
+        handling = dict(handling)
+        submit_upstream = handling.pop("submit_upstream", False)
+        provider_name = handling.pop("upstream_provider", None)
+        credentials = handling.pop("upstream_credentials", None) or {}
+        if submit_upstream and provider_name:
+            handling["upstream_providers"] = [provider_name]
+            handling["upstream_credentials"] = {provider_name: credentials}
+        return handling
+
 
 def collapse_activities(obj):
     """Utility method to replace the "activities" list in a spot or alert JSON object with a single "activity" value,