# Haiku 5.5 subagents need smaller contracts, not vague delegation

Why Haiku 5.5 subagents need bounded questions and checkable return artifacts before lower call costs can become useful task-level efficiency.

Author: Retrivium editorial team
Language: en
Analysis published: 2026-11-03
Event date: 2026-10-07
Original announcement: https://www.anthropic.com/claude-haiku-5-5
Canonical URL: https://retrivium.ai/retrospectives/haiku55-subagent-contract-size/

## A smaller model acquired a delegation role

[Opus 5.5 launched on September 22, 2026](https://www.anthropic.com/claude-opus-5-5), followed by [Sonnet 5.5 on September 28](https://www.anthropic.com/claude-sonnet-5-5). The [October 7 Haiku 5.5 announcement](https://www.anthropic.com/claude-haiku-5-5) positioned the smaller model for narrow, high-volume work and subagent roles. The important design implication is not that every task should be split. It is that an inexpensive specialist becomes useful when its assignment can be bounded and its output checked without recreating the entire investigation in the parent agent.

## A delegation needs an answer contract

An illustrative parent task prepares a dependency-upgrade assessment. A subagent can identify where a named library is imported and return file references with short contextual notes. That assignment has a clear input and a verifiable output. “Research everything relevant and recommend the upgrade” is much broader and leaves completion ambiguous. The narrower contract lets the parent integrate evidence while retaining responsibility for the final decision. It also prevents an attractive low per-call cost from encouraging an unlimited number of loosely defined investigations.

## Independence requires enough context

A specialist cannot answer accurately if the task omits the version, relevant repository boundary or meaning of the requested identifier. Yet forwarding the entire parent history can burden the specialist with unrelated assumptions. The useful handoff contains the facts needed for the bounded question and explicit uncertainty about missing facts. This is a general orchestration recommendation, not a model-specific guarantee. The objective is to reduce ambiguity at the delegation boundary while avoiding a miniature copy of the parent's whole assignment.

## An illustrative return artifact

A practical fixture provides a small repository with direct imports, an indirect wrapper and an unrelated string match. The specialist returns categorized references rather than a bare count. The parent checks the references against the fixture and verifies that the wrapper is not silently treated as proof of direct usage. No performance score is claimed. The artifact demonstrates why a checkable answer can be integrated cheaply, whereas a confident unstructured conclusion forces the parent to repeat the search before trusting it.

## Cost follows integration quality

Subagents add coordination, context transfer and review work. Their value depends on whether specialization reduces more work than those costs introduce. The October release makes narrow delegation worth exploring, but it does not establish a universal saving from parallelism or a fixed quality level for every subtask. The retrospective lesson is to define the return contract first, then choose a model and measure the complete path to an accepted parent result. A small specialist is most useful when its boundary makes responsibility clearer rather than merely distributing uncertainty.

## Related reading

- [Structured execution contracts](/journal/openrouter-tool-calling/)
- [Including coordination costs](/journal/inference-economics/)