kalshi-cpp follows Kalshi's published Predictions contracts. The copies in spec/ are byte-identical to what Kalshi served on 2026-09-25.

File	Version	SHA-256
`spec/openapi.yaml` from https://docs.kalshi.com/openapi.yaml	3.31.0	`7a870e939ec61793ff31d04e89c40a85246a82d5a60e0f3803a45806444baa97`
`spec/asyncapi.yaml` from https://docs.kalshi.com/asyncapi.yaml	2.0.0	`1fe32a4b7c63fe6b98b09cdb8a2510ae14cc09764c0679feb7d2fe772a023537`

Kalshi's Margin API (https://docs.kalshi.com/perps_openapi.yaml) has its own host, authentication, and risk model, so this client leaves it out.

Authentication

Each request signs timestamp_ms + METHOD + path with the account's key. The path starts at /trade-api/v2 (REST) or /trade-api/ws/v2 (WebSocket) and excludes the query string. The signature goes in KALSHI-ACCESS-SIGNATURE, next to KALSHI-ACCESS-KEY and KALSHI-ACCESS-TIMESTAMP. RSA keys sign with RSA-PSS and SHA-256; Ed25519 keys sign the message directly. See Kalshi's API keys guide.

Updating the contract

curl -fsS https://docs.kalshi.com/openapi.yaml -o spec/openapi.yaml
curl -fsS https://docs.kalshi.com/asyncapi.yaml -o spec/asyncapi.yaml
shasum -a 256 spec/*.yaml
make codegen test

Review the diff of the generated files, update the table above, and note user-visible changes in CHANGELOG.md. Kalshi's changelog at https://docs.kalshi.com/changelog explains most changes.