Swapping Tools Mid-Conversation Without Losing Your Prompt Cache
Tools can now be added and removed between turns, but the tool block sits at the very front of the cache prefix. I measured 12 mutation patterns with fingerprints and built a stable-core plus volatile-tail registry with a guard that refuses unsafe changes.
6 Traps I Hit Building In-App AI Chat with Claude API — A Record of Getting to Production
Six real design mistakes I encountered shipping Claude API in-app chat to production — covering context management, streaming error detection, guardrails, session persistence, model versioning, and cost monitoring. Includes working TypeScript code.
Combining Haiku 4.5, Streaming, and Prompt Caching to Cut Costs in a Personal App — An Implementation Record
A hands-on record of combining Claude Haiku 4.5, streaming, and prompt caching to improve both cost and response speed in a personal iOS/Android app — including the mistakes made along the way.
Build a Pipeline Where Docs Update Automatically Every Time Your Code Changes
Build a CI/CD pipeline that auto-generates README, CHANGELOG, and API docs whenever code changes. Use Claude Haiku 4.5 for cost-efficient classification and Sonnet 4.6 for quality output — cutting API costs by up to 70% while keeping documentation accurate.
Claude Sonnet 4.6 vs Opus 4.6 — A Task-by-Task Selection Guide From Daily Use
Choosing between Sonnet 4.6 and Opus 4.6 comes up more often than you'd expect. From someone who uses both daily, here's a task-by-task breakdown — plus how the same yardsticks carry over to Sonnet 5 and Opus 4.8, and where a narrower price gap moves the break-even.
Running Claude's Message Batches Overnight — What the 50% Discount Actually Covers
What I learned running Claude API Message Batches for real: what the 50% discount covers, the custom_id character restriction, and designing around the 24-hour window and 29-day retention.
Claude API Messages Batches: Cutting Production Costs by Up to 50% with Async Processing
Field notes from running the Claude API Messages Batches API in production. Polling design, composite custom_id keys, the 29-day window that starts at created_at rather than completion, and the cost numbers recomputed from current published prices.
When to Use Claude Code's Native 1M Context — and When Not To: A Cost-Based Rule
With Sonnet 5 as the default, Claude Code now handles a native 1M-token context. A big window is convenient, but every token you park in it is billed again each turn. Should you load the whole repo, or feed slices? Here is an estimable token model and a decision rule that gives a concrete answer per situation, with working code and the traps to avoid.
Introductory Pricing Has an End Date — Effective-Dated Cost Forecasts for the Sonnet 5 Price Step
Claude Sonnet 5's introductory $2/$10 pricing ends on 2026-08-31 and reverts to $3/$15. A static price map will quietly understate your September forecast by a third. Here is an effective-dated price table and forecast design that absorbs the step.
When Claude API Document Extraction Is Confidently Wrong — Field Notes on Catching Silent Errors with Invariants
In structured extraction from invoices and contracts, the real danger isn't a crash — it's a value that's silently wrong while the schema validates and confidence reads high. Field notes on invariants, two-pass extraction, and tracking field-level error rates.
Stop rebuilding intermediate files every request: reuse the Code Execution container to carry pipeline state
How to reuse the Code Execution container across requests by passing its container ID, so generated files and intermediate results carry over to the next step. Includes the execution-time billing trap and how to handle container_expired safely, with working code.
Every Tool Call Succeeds, Yet Nothing Moves Forward: Detecting Stagnation in Unattended Agents
No errors, yet the agent keeps replaying the same move while your budget quietly drains. Here is how to detect a success-but-no-progress loop using a progress oracle and action fingerprints, with a working Python implementation that halts safely.