Blog

Engineering

429 Retry-After: Stopping a Rate-Limit Retry Storm

A Mythos V3 engineering case study on adding correct 429 Retry-After headers, separating quota gates, and reducing five-minute application 429s from 1,050 to 7.

2026-08-21 8

Yazhou Hu

Engineering

Node.js Event Loop Blocking: Fixing an O(n²) Prefix-Hash Hot Path

A Mythos V3 engineering note on diagnosing Node.js event loop blocking, replacing quadratic prefix hashing with one linear pass, and proving byte-for-byte equivalence.

2026-08-21 9

Yazhou Hu

Guide

Claude Opus 5 API: Model ID, Setup, and Context Window Guide

The exact claude-opus-5 model ID, environment setup, context window, and copy-pasteable API requests for Claude Code and the Anthropic Messages API.

2026-08-14 7

Yazhou Hu

Comparison

Claude Opus 5 vs Fable 5: Which to Use in 2026

Claude Opus 5 vs Fable 5: same 1M context and 128K output, but Fable costs 2x at list. A decision table for picking the right Claude model in 2026.

2026-08-11 7

Yazhou Hu

Guide

Claude API Pay-As-You-Go: Costs, Billing and Setup

Understand metered Claude API costs, compare billing options, check model access, and connect the right endpoint and key before making your first request.

2026-06-30 6

LLM API Editorial Team

Guide

DeepSeek + Qwen in Claude Code: One Key, Many Models

DeepSeek Claude Code setup: use DeepSeek and Qwen through one relay key and shared wallet — learn when each model makes sense and how billing works.

2026-06-30 7

Yazhou Hu

Guide

Anthropic API Rate Limits & Usage Tiers Explained (2026)

How Claude API rate limits work in 2026: RPM, ITPM, and OTPM; the four spend-based usage tiers and how you advance; why cached reads don't count; and how to handle 429s.

2026-06-29 8

Yazhou Hu

Tutorial

ANTHROPIC_BASE_URL: Claude Code Setup and /v1 Fixes

Set ANTHROPIC_BASE_URL correctly for Claude Code on Windows, macOS and Linux. Compare base URLs with request endpoints and diagnose 404, authentication and quota errors.

2026-06-28 4

LLM API Editorial Team

Comparison

Cheap Claude API Access in 2026: The Legit Ways to Pay Less

The real ways to get cheaper Claude API access in 2026 — right-sizing the model, prompt caching, batch, subscription vs pay-as-you-go, and relays — with an honest look at the trade-offs of each.

2026-06-27 8

Yazhou Hu

Guide

Claude Code Token Cost: Why It Climbs and How to Cut It

Claude Code token cost grows super-linearly because context is re-sent every turn. Here's why long sessions get expensive and the concrete levers to cut spend.

2026-06-23 7

Yazhou Hu

Guide

What Is a Claude-Compatible API Relay? A Plain Explainer

A claude compatible api relay speaks the same endpoints Claude Code already uses. Here's how relays work, why your CLI can't tell, and whether to trust one.

2026-06-16 7

Yazhou Hu

Comparison

Claude Sonnet 4.6 vs Opus 4.8 in Claude Code: Which to Run

Claude Sonnet 4.6 vs Opus 4.8 for Claude Code: Sonnet is cheaper and faster for daily coding; Opus 4.8 wins hard refactors and architecture. Task-by-task picks, token cost, and the in-session /model switch.

2026-06-09 7

Yazhou Hu

Comparison

Claude Code vs Codex CLI in 2026: An Honest Head-to-Head

Claude Code vs Codex CLI compared on workflow, protocol, and config — run both agentic coding CLIs off one sk-relay key because we expose both protocols.

2026-06-06 8

Yazhou Hu

Guide

Claude Opus 4.8 in Claude Code: Setup, the 1M Context Window, and What It Costs

Run Claude Opus 4.8 in Claude Code: exact model IDs, the ANTHROPIC_BASE_URL setup, whether the 1M-token context window is still available, and how to keep the bill down.

2026-06-06 7

Yazhou Hu

Troubleshooting

Fix a Claude Code Connection Error or Timeout: A Diagnostic Ladder

A Claude Code connection error or timeout usually has a boring cause. Here's the diagnostic ladder to tell a real network/config fault from the model thinking.

2026-06-06 7

Yazhou Hu

Comparison

Claude Code Pricing in 2026: Pro vs Max vs Pay-As-You-Go API

A plain-English breakdown of what Claude Code actually costs in 2026 — the official Pro and Max subscription tiers, how token-metered API billing compares, and when a relay subscription at a fraction of the price makes sense.

2026-06-05 8

Yazhou Hu

Tutorial

Using Cline and Roo Code with a Claude-Compatible API

Step-by-step setup for pointing Cline and Roo Code — the VS Code AI coding extensions — at an Anthropic-compatible relay. Provider settings, base URL, model IDs, and the gotchas with OpenAI-compatible vs native Anthropic mode.

2026-06-04 7

Yazhou Hu

Announcement

Codex CLI, OpenAI SDK & LiteLLM with Claude: OpenAI-Compatible Setup

Point Codex CLI, the OpenAI SDK, or LiteLLM at Claude models with one OpenAI-compatible key. Exact /v1/responses and /v1/chat/completions setup, the wire_api gotcha, and a Codex config.toml walkthrough.

2026-05-15 6

Yazhou Hu

Engineering Notes

A 15-Second CPU Stall From One Unclosed XML Tag

Postmortem on a relay process that pegged a single core for fifteen seconds straight. Catastrophic regex backtracking on user-controlled input. Three-character fix, three-layer defense (bounded quantifier + per-request watchdog + nginx next_upstream).

2026-05-06 9

Yazhou Hu

Engineering Notes

Reasoning Blocks at the Relay: What Changes When the Upstream Emits Thinking

Open-weight reasoning models (DeepSeek V3.x, MiniMax M-series, Qwen3 reasoning) now ship interleaved thinking blocks. Notes on translating that to Claude Code's Anthropic-protocol contract — block ordering, signature handling, tool-use interleaving, and SSE shape.

2026-05-06 10

Yazhou Hu