DeepSeek Harness 0.1.5 is a migration-sensitive pre-release, not a routine interface update. The substantive changes landed in dsh-v0.1.5-rc.1 on September 10, 2026: Session data moves to V3, default tool sets change, subagents become easier to continue and steer, file workflows expand, and several SDK and plugin contracts change.
DeepSeek published dsh-v0.1.5-rc.2 later on September 10. It is the latest official pre-release as of September 11, but it adds only two small user-experience refinements: clearer feedback submission behavior and cleaner delivered-file presentation. It does not replace the need to read the RC1 migration notes.
Last verified: September 11, 2026. This article describes the upstream DeepSeek Harness releases. It does not claim that Agent.Space runs or supports either 0.1.5 release candidate.
DeepSeek Harness 0.1.5 in one minute
If you are coming from the 0.1.2 line, keep the 0.1.2 RC1 article as historical context. The rest of this guide focuses on the upgrade decisions introduced by 0.1.5 RC1 and preserved in RC2.
What changes for users
File work becomes more visible and flexible
The 0.1.5 RC1 Web interface accepts arbitrary file uploads, keeps uploads active when the user switches conversations, and lets the model read the resulting saved paths through file tools. The new right sidebar can show Markdown, code, HTML, PDFs, and images in tabs or split panes. Delivered files can also be previewed, opened, or revealed in an external application.
That can make an output easier to inspect, especially when a task produces several artifacts. It also widens the practical data boundary. Before uploading a file, confirm that it belongs in the test environment and that the enabled model, plugins, tools, and external applications are allowed to access it.
Long sessions and continuable subagents get more control
RC1 extends continuable subagents with queued follow-ups, message editing and deletion, steering for one or all active children, and stop controls. It also includes long-conversation performance and memory work, lazy loading for older conversation references, and refinements to team-message attribution and ordering.
These controls are useful for correcting a delegated task without discarding it. They are not a substitute for a bounded brief. A child that can continue, receive new instructions, and access tools can also remain active longer than expected, so the operator still needs explicit scope, permissions, and stop conditions. The safe evaluation workflow turns those boundaries into a repeatable first test.
Model and provider setup becomes broader
The official DeepSeek model adapter adds DeepSeek-V41-Flash under the deepseek-flash identifier and makes it the default for new sessions unless a model is explicitly configured. The release also adds model discovery from a custom provider's models object and from Anthropic's native model listing, including display names and context/output limits where available.
Outbound requests can now honor HTTP_PROXY, HTTPS_PROXY, ALL_PROXY, and NO_PROXY. That helps installations that require a proxy, but it does not make the destination or data flow safe by itself. Verify the resolved model, provider, base URL, proxy path, credentials, and billing route rather than inferring them from a model label.
Dynamic system-prompt updates are also supported without invalidating the KV cache, but only for models that declare support. Integrations should treat that declaration as a capability check, not assume the behavior for every model.
Session V3 is the upgrade gate
The most consequential 0.1.5 change is the Session data format V3. DeepSeek says supported older logs are migrated into new files while the originals are preserved. Upgraded Session data cannot be read by older versions, so downgrading that data is not supported.
That creates four checks before installation:
- Back up any Session data that matters outside the working directory.
- Test migration on a copied, non-sensitive Session set before touching the only copy.
- Keep the previous pinned environment until the migrated data and recovery path have been verified.
- Update custom log readers, exporters, dashboards, or plugins that depend on the old format.
The session lifecycle API changes too. Code that creates or controls sessions may need to adopt SessionHandle; agentLoop.create() is asynchronous; and a Session lock permits at most one process to own a Session. Test startup, resume, pause, cancellation, and concurrent access instead of checking only whether the UI opens.
Default tools and plugin APIs changed
RC1 changes which tools are present by default across execution surfaces:
The Bash tool also reports exit and timeout information more explicitly. Treat these as effective-runtime facts to record in an evaluation; do not reuse a tool inventory from an older tag.
Plugin maintainers have additional migration work. RC1 removes ctx.agent from the Agent plugin API in favor of passing the agent explicitly, reshapes Inbox access around agent.inbox, and changes Web panel and conversation-slot APIs. The experimental Agent Teams package requires an explicit profile and is not a default capability. Review custom plugins against the exact RC2 package and test their least-privilege behavior before re-enabling them.
The security boundary did not change
DeepSeek still labels the official repository as a Developer Preview. Its Safety Notice says the project has not undergone a security audit and should not be treated as secure or production-ready.
The harness can execute code and commands, load plugins, and reach files, processes, networks, and credentials exposed by its environment. Sandboxes, approvals, and permission controls can reduce risk but do not guarantee isolation. File uploads, external “Open in” actions, persistent shells, proxies, and continuable subagents all deserve the same least-privilege review as any other tool path.
Use a disposable virtual machine or container, provide only test-scoped credentials and data, keep recoverable backups, and inspect every plugin, configuration change, and proposed command. The broader coding-agent workspace security guide provides a surface-by-surface checklist.
A practical 0.1.5 upgrade checklist
Before upgrading:
- record the current package, tag or commit, launch profile, model/provider configuration, plugins, tools, and environment;
- back up Session data and test a V3 migration on a copy;
- find custom readers and code that depend on Session, Agent, Inbox, Web panel, or editor APIs;
- confirm the new default tool set for the exact surface you use;
- create a disposable test environment with restricted files, network, processes, and credentials.
During the test:
- pin
dsh-v0.1.5-rc.2rather than a moving branch or unrecorded package resolution; - migrate one representative Session and verify open, resume, append, pause, cancel, and lock behavior;
- test one bounded file task and inspect uploads, saved paths, delivered files, and external-open actions;
- start, steer, and stop one continuable subagent while checking its permissions and message attribution;
- verify the actual model, provider, proxy route, tools, and plugin set shown at runtime.
Before adoption:
- compare the filesystem and Session artifacts with the backed-up baseline;
- run independent tests rather than accepting the final chat response as proof;
- confirm that custom integrations no longer use removed contracts;
- keep a rollback environment even though migrated Sessions themselves cannot be downgraded;
- document which RC2 capabilities passed and which remain untested.
What this means for Agent.Space
The 0.1.5 RC releases describe the upstream open-source project. They do not establish the version, tools, Session format, default model, plugins, or subagent behavior currently available through Agent.Space.
For that distinction, read what DeepSeek Harness means on Agent.Space and check the current DeepSeek Harness Agent page. Treat the product interface as the source of truth for hosted availability; treat the official release tags as the source of truth for an upstream installation you control.
Frequently asked questions
What is the latest DeepSeek Harness release?
As verified on September 11, 2026, dsh-v0.1.5-rc.2 is the newest GitHub pre-release. Because the project is moving quickly, verify the Releases page again before installing.
What is the difference between 0.1.5 RC1 and RC2?
RC1 contains the major features and breaking changes. RC2 is a small follow-up that improves feedback submission behavior and delivered-file presentation. An RC2 evaluation still needs the RC1 migration checklist.
Can an upgraded Session be opened in an older version?
DeepSeek says upgraded Session data cannot be downgraded. Preserve originals and test V3 migration on a copy before relying on it.
Does Agent.Space support DeepSeek Harness 0.1.5 RC2?
This article makes no such claim. Check the current Agent.Space interface and product materials for hosted availability and behavior.
The practical takeaway
DeepSeek Harness 0.1.5 RC2 is the version to pin for a current pre-release evaluation, but RC1 is the document that explains why the upgrade needs care. Protect Session data first, re-audit defaults and plugin contracts, and test the exact runtime in an isolated environment.
If DeepSeek Harness is shown for your workspace, open Agent.Space, confirm the available Agent and model choices separately, and begin with one bounded task you can inspect and reverse.