Inside the Claude family, the most common decision is Sonnet or Haiku. Opus is reserved for the hard stuff. Sonnet is the workhorse. Haiku is the fast-and-cheap. Picking right per task is the simplest 30-50% cost optimization most developers never make.
Best balance of speed and intelligence — production default.
Fastest and cheapest Claude — high-volume workhorse.
Haiku handles factual chat, simple Q&A, and quick lookups perfectly. Sonnet is overkill — pay 3x for marginal quality.
Both write good code for one function. Sonnet edges ahead on edge cases and idiomatic patterns. Haiku is faster and cheaper. Pick speed (Haiku) or thoroughness (Sonnet).
Sonnet wins clearly. Multi-step reasoning, cross-file consistency, edge-case handling — Haiku misses things Sonnet catches.
Sonnet is every agent's recommended default. Haiku is OK for lightweight agents but drops the ball on long autonomous chains.
Haiku is the right tool — cheap, fast, good enough for one-task subagents like 'grep this dir', 'summarize this file', 'check for X'.
Haiku at $0.12/M input (Pro) lets you process millions of items cheaply. Sonnet at $0.36/M is 3x more — overkill for classification.
Default to Sonnet 4.6 for any agent main loop, multi-file work, or anything requiring deeper reasoning. Switch to Haiku 4.5 for chat, single-function code gen, classification, fan-out subagents, and high-volume jobs. The smart pattern: Sonnet for the spine, Haiku for the limbs.
claudeapi.cheap Pro plan: Sonnet 4.6 = $0.36 input / $1.80 output per 1M. Haiku 4.5 = $0.12 input / $0.60 output per 1M. Both 80% off official. Mixing them per task can save you another 50-70% on top of our discount.
Get a free API keyYou can, but you'll see quality drop on multi-step tasks. Most agents (Claude Code, Cline, Cursor) recommend Sonnet for the main loop and Haiku for subagent fan-out. Try Haiku for a day on your real workflow — if it works for your use case, great. If you see drift or missed steps, switch back to Sonnet.
Realistic example: an agent that does 80% Sonnet (main reasoning) + 20% Haiku (file scans, classifications). Sonnet-only cost: $1.00. Mixed cost: ~$0.65. Combined with claudeapi.cheap's 80% off, you're at $0.13/$1 — incredibly cheap for a real coding agent.
Yes. Same Anthropic API, same context window, same tool-call format, same streaming. The only thing that changes is the model id: claude-sonnet-4-6 vs claude-haiku-4-5. Switch in one line.
Opus 4.7 for hard architectural decisions, novel problems Sonnet drifts on, or when you need 128k max output. Default = Sonnet. Escalate = Opus. Drop down = Haiku.