gamma-api keyset endpoints: cursor parameter ignored, returns same first page #227

Summary

Both gamma-api.polymarket.com/markets/keyset and gamma-api.polymarket.com/events/keyset return HTTP 200 with a populated next_cursor, but passing that next_cursor back as cursor=... on the next request returns the same first-page items. The cursor parameter appears to be ignored server-side.

This blocks every client preparing for the May 1 2026 sunset of the legacy /markets, /events list endpoints, since the keyset endpoints are the documented replacement.

Reproducer

# Page 1, no cursor.
curl -s "https://gamma-api.polymarket.com/markets/keyset?limit=2" \
  | python -c "import json,sys; d=json.load(sys.stdin); print('ids:', [m['id'] for m in d['markets']]); print('next_cursor:', d['next_cursor'][:40] + '...')"

# Page 2, using the next_cursor from page 1.
NXT=$(curl -s "https://gamma-api.polymarket.com/markets/keyset?limit=2" \
  | python -c "import json,sys; print(json.load(sys.stdin)['next_cursor'])")
curl -s "https://gamma-api.polymarket.com/markets/keyset?limit=2&cursor=${NXT}" \
  | python -c "import json,sys; d=json.load(sys.stdin); print('ids:', [m['id'] for m in d['markets']]); print('next_cursor:', d['next_cursor'][:40] + '...')"

Expected: page 2 returns ids strictly different from page 1 (advancing the keyset).
Observed: page 2 returns the identical ids and the identical next_cursor.

Same behavior on /events/keyset. Reproducible from any IP at the time of writing (2026-04-27).

What I've ruled out

• URL encoding of the cursor (with and without urlencode)
• Cursor parameter name (cursor, next_cursor, after all behave identically)
• Transport (POST body and X-Cursor header don't help)
• Cloudflare cache (cache-buster _=$RANDOM produces cf-cache-status: MISS but the server still returns the same first page)
• Filter combinations (with and without closed=false, order=id, ascending=false — all loop)
• Decoding the cursor confirms it correctly encodes the last-seen id, e.g.:

  {"v":1,"k":"markets","oh":"...","keys":[{"t":"string","v":"540817"}]}

  so the server is correctly producing the cursor — it just isn't honoring the cursor on the next request.

A multi-page walk against /markets/keyset exhausts at 200 pages, returning ~1,000 unique markets and ~199,000 duplicates (every page is page 1).

Cross-check: CLOB cursor works

For comparison, clob.polymarket.com/markets cursor pagination works correctly:

NXT=$(curl -s "https://clob.polymarket.com/markets" | python -c "import json,sys; print(json.load(sys.stdin)['next_cursor'])")
# NXT = "MTAwMA==" (decodes to "1000")
curl -s "https://clob.polymarket.com/markets?next_cursor=${NXT}" | python -c "import json,sys; print(json.load(sys.stdin)['next_cursor'])"
# Returns "MjAwMA==" (decodes to "2000") — cursor advances correctly.

So this is gamma-keyset-specific; not a general issue with cursor handling at Polymarket.

Asks

1. Is this a known issue? I haven't found a tracking item.
2. ETA on a fix relative to the May 1 2026 sunset of /markets and /events? If the cursor stays broken when legacy sunsets, every keyset client loses pagination simultaneously.
3. Any documented workaround on the keyset endpoints? (Alternative pagination parameter name, or a documented requirement I've missed.)
4. If no near-term fix is planned, is clob.polymarket.com/markets (whose cursor works) a supported alternative source for the full market universe? It returns a different shape so clients would need to map.

Happy to provide more diagnostic data — full request/response captures, cursor base64 decodes, etc. — if useful.