Perps (margin) API — full SDK implementation

Implements the Kalshi Perps API (perpetual futures / margin) in the SDK, mirroring the conventions of the existing prediction (event-contract) API. Source docs: https://docs.kalshi.com/margin

Surface (3 separate specs + FIX)

Locked architecture decisions

• Standalone PerpsClient / AsyncPerpsClient (not a namespace on KalshiClient). Own base URL, own PerpsConfig, separate env-var credentials. Reuse KalshiAuth (RSA-PSS) + SyncTransport/AsyncTransport + retry/error machinery unchanged. (Rationale: different host + Kalshi recommends separate API keys; KalshiConfig hard-fails on hosts outside its known set.)
• New package layout kalshi/perps/{client,async_client}.py, kalshi/perps/models/<area>.py, kalshi/perps/resources/<area>.py, kalshi/perps/ws/… — mirroring the top-level layout. Exports flow kalshi/perps/__init__.py → kalshi/__init__.py.
• Reuse DollarDecimal + FixedPointCount from kalshi/types.py: perps FixedPointDollars (string, ≤6 dp) and FixedPointCount (string "fp", 2 dp) have identical semantics. Prices/counts use them with validation_alias=AliasChoices(...) for API↔Python name mapping.
• Timestamps: REST = RFC3339 date-time; WebSocket = Unix epoch milliseconds with _ms suffix (ts_ms, created_ts_ms) — a real parsing difference from the event-contract WS.
• Request bodies = Pydantic models with model_config = {"extra": "forbid"}, serialized via model_dump(exclude_none=True, by_alias=True, mode="json"); serialization_alias for wire mismatches. POST/PUT/DELETE never retried.
• Contract tests parameterized per-spec: perps REST validates against specs/perps_openapi.yaml, SCM against specs/perps_scm_openapi.yaml. Weekly spec-sync extended to fetch all three perps specs.

Shared-primitive ownership (avoid duplicate Pydantic defs)

The shared enums/value-objects — BookSide, SelfTradePreventionType, LastUpdateReason, OrderSource, MarginMarketStatus, ExchangeIndex, ExchangeInstance, PriceLevelDollarsCountFp, EmptyResponse, ErrorResponse — are defined once by the foundation issue in kalshi/perps/models/common.py. All resource issues import them and must not redefine. (Note: perps order side is bid/ask, not the prediction API's yes/no.)

Dependency graph

graph TD
  F[#388 foundation] --> EX[#389 exchange]
  F --> MK[#390 markets]
  F --> OR[#391 orders]
  F --> OG[#392 order groups]
  F --> PF[#393 positions/fills/trades]
  F --> BR[#394 balance/risk/fees]
  F --> FN[#395 funding]
  F --> TR[#396 transfers/subaccounts]
  F --> WF[#397 ws foundation]
  WF --> WC[#398 ws channels]
  F --> SA[#399 scm auth]
  SA --> SE[#400 scm endpoints]
  EX --> DOC[#401 docs/release]
  MK --> DOC
  OR --> DOC
  OG --> DOC
  PF --> DOC
  BR --> DOC
  FN --> DOC
  TR --> DOC
  WC --> DOC
  SE --> DOC

Implementation checklist

Foundation (do first)

• perps: client foundation — PerpsClient/AsyncPerpsClient, PerpsConfig, spec sync & contract-test harness #388 — client foundation: PerpsClient/AsyncPerpsClient, PerpsConfig, spec vendoring, contract-test harness parameterization, common.py

REST resources (depend on #388, parallelizable)

• perps: exchange status, enabled flag & risk parameters resource #389 — exchange status, enabled, risk parameters
• perps: markets resource — list/get, orderbook, candlesticks #390 — markets: list/get, orderbook, candlesticks
• perps: orders resource — create/get/list/cancel/decrease/amend + FCM orders #391 — orders: create/get/list/cancel/decrease/amend + FCM orders
• perps: order groups resource — create/get/list/delete/reset/trigger/update-limit #392 — order groups: create/get/list/delete/reset/trigger/update-limit
• perps: portfolio reads — positions, fills, trades #393 — portfolio reads: positions, fills, trades
• perps: balance, risk, notional risk limit & fee tiers resource #394 — balance, risk, notional risk limit, fee tiers
• perps: funding resource — rate estimate, historical rates, payment history #395 — funding: rate estimate, historical rates, payment history
• perps: transfers & subaccounts resource — intra-exchange-instance transfer, create/transfer margin subaccount #396 — transfers & subaccounts: intra-exchange-instance transfer, create/transfer subaccount

WebSocket (after REST foundation)

• perps: WebSocket foundation — connection, client, subscribe/dispatch framing, sequence/orderbook reuse #397 — WS foundation: connection, client, subscribe/dispatch framing, sequence/orderbook reuse
• perps: WebSocket channels & payload models — orderbook_delta, ticker(+funding), trade, fill, user_orders, order_group_updates #398 — WS channels & payload models: orderbook_delta, ticker(+funding), trade, fill, user_orders, order_group_updates

SCM / Klear (new session+MFA auth)

• perps: SCM/Klear auth foundation — KlearClient with session-cookie + MFA login #399 — KlearClient auth foundation: session-cookie + MFA login
• perps: SCM/Klear margin endpoints — settlement balances, obligations, margin reports #400 — SCM endpoints: settlement balances, obligations, margin reports

Closeout

• perps: docs, examples, README/CHANGELOG, demo integration tests & release closeout #401 — docs, examples, README/CHANGELOG, demo integration tests & release

Out of scope (this milestone)

• FIX API → tracked separately in perps: [EPIC] FIX API support (prediction + perps) — future #402 (covers both prediction and perps FIX gateways; large, orthogonal effort).
• Perps WS channels unavailable upstream (market_positions, market_lifecycle_v2, multivariate*, communications) — documented, not implemented.
• Batch order ops, RFQs/quotes, events/series/milestones on the margin exchange (not offered by the perps API).