LangChain.js shipped @langchain/[email protected] on 2026-09-27: ports explicit prompt-cache options across Chat Completions and Responses, preserves content-block breakpoints, and maps cache-write usage to cache_creation. A same-tag fix serializes promptCacheRetention: "in-memory" as API-legal "in_memory" and unifies precedence (per-call → modelKwargs → constructor); Chat Completions no longer drops modelKwargs.
Key Takeaways
- ✓Shipped: @langchain/[email protected] / npm 1.6.0
- ✓Explicit prompt cache options + content-block breakpoints; cache-write → cache_creation (PR #11232)
- ✓Fix: serialize in-memory as in_memory; precedence per-call > modelKwargs > constructor (PR #11735)
- ✓Install: npm i @langchain/[email protected]
- ✓Follow-on: @langchain/[email protected] bumps this dependency the same day
Project Links & Resources
Direct AccessIn-Depth Technical Analysis
Core Background & Industry Pain Points
Without explicit prompt-cache plumbing, LangChain.js apps overpay on repeated long prefixes; hyphenated in-memory retention values were rejected by the API.
Architecture Highlights & Internals
@langchain/[email protected] (PR #11232) forwards explicit cache options on Completions and Responses, keeps content-block breakpoints, and maps cache-write usage to cache_creation. PR #11735 serializes in-memory→in_memory and fixes precedence plus Chat Completions modelKwargs.
Authoritative Benchmarks & Measured Scores
No public latency/cost leaderboard in the release notes. Compare cache_creation/cache-read tokens and bills on a fixed long-prefix script before/after upgrade.
Developer Hands-on Guide
npm i @langchain/[email protected]. Pass promptCacheOptions / key / retention per the Chat OpenAI docs. Bump @langchain/xai to 1.4.15 if needed.
Discussion & Comments
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