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Callosum
Orchestration layer that routes AI work across many models and many chips
Last verified August 25, 2026 · Updated daily
What Callosum is building
Callosum builds the orchestration layer for heterogeneous compute. The bet is that an AI workload is not one thing: it is a workflow problem (how you define the job), an agent problem (which models you call), and a hardware problem (which silicon each of those calls should land on). Today almost everyone answers all three with the same answer, a frontier model on a rack of identical GPUs. Callosum's software decomposes the request and routes each piece to the model and chip actually suited to it. The technical surface is wide because the problem is vertical. The company works from the AI systems layer down to the compile level, and the open roles map the stack exactly: inference engine, accelerator systems software, cloud resource orchestration, networking and interconnect, evolutionary optimisation, agent runtime, benchmarking and evals. Partnerships with Cerebras, Rebellions, Axelera, Tendrils and Supermicro are the other half of the work, because routing to a chip means having tested real workflows on that chip first. The intellectual root is the founders' actual research. Danyal Akarca and Jascha Achterberg spent their Cambridge PhDs on how brains achieve flexible cognition by combining many specialised circuits rather than scaling one uniform one, publishing in Nature journals with Google DeepMind and Intel Labs. Callosum is that finding turned into infrastructure. Akarca's framing in the round announcement: "The industry has been betting that one model or one chip will rule them all. But nature shows us the opposite. Intelligence is collective and will emerge from many specialised systems working together." Achterberg puts the sovereignty argument more bluntly: "AI sovereignty isn't about owning a chip fab. It's about never being hostage to one." That sentence is why the UK's Sovereign AI Fund made Callosum its first disclosed investment since launching in April 2026.
Why this matters
The numbers Callosum publishes are the argument. On agentic financial-services workloads, its production platform reports 4x faster performance, a 70% cost reduction, and a 10 percentage-point improvement in task success rate against a single frontier model on GPU. Plural's investment note cites 2x accuracy, 7x speed and 4x lower cost on autonomous computer-use tasks. Those are the company's own figures, not third-party benchmarks, but they are specific and falsifiable, which is more than most infrastructure pitches manage. The structural case is that inference is disaggregating. A record wave of semiconductor startups is shipping real silicon (Cerebras, Rebellions, Axelera among Callosum's partners), and none of it inherits CUDA's software gravity. Someone has to be the layer that makes a mixed fleet usable, the way VMware made a mixed server fleet usable in the 2000s. If that layer is a neutral third party rather than a chip vendor, the economics of running AI change for everyone downstream. There is also a political tailwind that is unusual for a seed company. Being the UK Sovereign AI Fund's first disclosed cheque, and a founding member of ARIA's Scaling Inference Lab, means Callosum is not just a startup with a thesis; it is the thing the UK is pointing at when it talks about not being dependent on one vendor's stack.
Open roles at Callosum
11 positions we're tracking. Roles are re-checked daily and removed when filled.
Inference Engine — Member of Technical Staff (London)
First seen today
Accelerator Systems Software — Member of Technical Staff (London)
First seen today
Cloud Systems & Resource Orchestration — Member of Technical Staff (London)
First seen today
Networking & Interconnect Systems — Member of Technical Staff (London)
First seen today
Evolutionary Optimisation — Member of Technical Staff (London)
First seen today
Agent Runtime & Systems — Member of Technical Staff (London)
First seen today
Research Engineer, Benchmarking — Member of Technical Staff (London)
First seen today
Research Engineer, Evals — Member of Technical Staff (London)
First seen today
ML Research Scientist / ML Research Engineer (London)
First seen today
Head of Physical Infrastructure (London)
First seen today
Chief of Staff, CTO (London)
First seen today
Know when Callosum is hiring before anyone else
A role stays uncontested for about four days. Here's the window — and where we put you in it.
From $9/month, cancel any time.
Watching Callosum
0 applicantsRole spotted & verified
1You get the alert
1You've applied
~8Hits the job boards
250+Hiring outlook
The strongest hiring signal in this drop. The round announcement explicitly allocates capital to "expand the team," and callosum.com/join-us currently lists 19 open roles, all London, all full-time. This is a company that raised $100M with a team assembled in under a year and is now hiring across every layer of its own stack at once.
Working at Callosum
Since , Callosum has built Orchestration layer that routes AI work across many models and many chips. The team is now people. For a AI company this size, the reality is opportunity to shape your role based on the company stage.
The majority of roles are in London.
How to actually get hired at Callosum
Why applying the normal way doesn't work
Callosum runs an applicant tracking system, but hiring managers still work referrals first. A cold application to Callosum isn't dead, it's just fourth in line behind internal referrals, sourced candidates and recruiter pipelines.
Who to contact at Callosum
What to show them
Build a small, honest benchmark that compares a heterogeneous model-and-hardware pipeline against a single frontier model on one agentic task — computer use, or a document workflow. Report accuracy, wall-clock, and dollars, and be explicit about where the heterogeneous route loses. Callosum publishes 4x/70%/10-point claims; the person who can make those claims survive an adversarial reviewer is the person they need.
A cold email that works at Callosum
What Callosum screens for
Atomico led, Plural and DCVC followed, and the UK Sovereign AI Fund made this its first disclosed investment. Read together, that is not a bet on a model — it is a bet that the inference layer fragments and someone neutral gets to arbitrate it. Sasha Vidiborskiy's line was that Callosum's vision could "fundamentally reshape how AI is deployed at scale." For a candidate, the window is narrow and obvious: a company that went from pre-seed to $100M in six months and opened 19 London roles at once is hiring faster than its brand recognition, which is exactly the moment when a specific, technical, non-generic application gets read by a founder rather than a recruiter.
Customize your CV for the Callosum role. Matching the job description language helps clear ATS filters.
Don't make these mistakes
Danyal trained as a medical doctor before his Cambridge computational neuroscience PhD, and he and Jascha have published extensively on how specialised circuits combine into intelligence. Opening with 'brain-inspired computing is fascinating' hands them their own abstract back. Skip the Nvidia-monoculture monologue too: Atomico, DCVC and the UK Sovereign AI Fund have already read that memo and written cheques against it. Also resist framing yourself as an 'AI generalist' — the 19 roles are aggressively specific, from compile-level accelerator work to interconnect. Lead with something you have personally made run on non-CUDA silicon, a scheduler heuristic that beat naive routing, or a benchmark where a small model on cheap hardware beat a frontier model on a task that mattered.
Mistakes that kill Callosum applications
A recycled CV gets rejected fast at Callosum ( people). They notice.
Skip 'I'm looking for...' — start with The numbers Callosum publishes are the argument and your specific angle on solving it.
Applying and waiting = silence. Follow up at day five — it roughly doubles your odds of a reply.
Applying to Callosum? Get the contact, not the form.
The Callosum interview process
4 stages · 14 days typical · take-home: yes · modelled from similar companies
We don't yet have verified candidate reports for Callosum. What follows is the typical process for a -person AI company — treat it as a model, not confirmed detail.
Interview stages
Recruiter Screen
Phone or video · 30 min
Basic qualification and logistics
Recruiter or HR
Hiring Manager Interview
Video call · 45 min
Role fit and experience deep-dive
Hiring manager
Technical/Functional Round
Video call · 60 min
Skills assessment and problem-solving
Team members
Final Round
In-person or video · 60 min
Culture fit and cross-functional alignment
Senior leadership
Callosum take-home assignment
Callosum includes a take-home exercise in their interview process. For AI roles, this typically involves a practical problem that takes 2-4 hours. Focus on clean, working code over premature optimization. They're evaluating how you think and communicate, not just the solution.
Callosum interview timeline
Timeline: ~ days. That's about average than the AI median (14 days at people).
Interviewed at Callosum?
Tell us how it went — stages, questions, timeline. Takes 90 seconds and it's how this page stays accurate for the next person.
Submit your Callosum interview experience →Callosum jobs, frequently asked questions
How many jobs does Callosum have open?
11 open roles at Callosum, last checked August 2026.
Does Callosum hire remotely?
Callosum doesn't have remote openings at the moment. All roles are in London.
What roles is Callosum hiring for?
Callosum is hiring across Other, Engineering, Operations. The most recent opening is Inference Engine — Member of Technical Staff (London).
How do I apply for a job at Callosum?
Use the apply links above, or check our guide to getting hired at Callosum.
Does Callosum respond to cold emails?
Not enough data yet on Callosum's cold email response rates.
Who is the hiring manager at Callosum?
At this size, hiring is usually run by the hiring manager.
How competitive is it to get hired at Callosum?
Expect 100-250 applicants in the first two weeks for AI roles at this size. Apply within 72 hours for best odds.
How many rounds is the Callosum interview?
4 stages: Recruiter Screen, Hiring Manager Interview, Technical/Functional Round, Final Round.
Is the Callosum interview hard?
Focus on technical depth and system design, not puzzles. Technical Interview is reportedly the most challenging round.
Does Callosum give a take-home task?
Yes, Callosum includes a take-home assignment.
How long does Callosum take to get back to you?
Around 14 days across the full process.
What should I prepare for the Callosum interview?
technical depth and system design is the priority. Show you can work autonomously — that matters more than algorithms at people.
Where is Callosum based?
Callosum is headquartered in London, US.
Get Callosum roles before they're posted
A role stays uncontested for about four days. Here's the window — and where we put you in it.
From $9/month, cancel any time.
Watching Callosum
0 applicantsRole spotted & verified
1You get the alert
1You've applied
~8Hits the job boards
250+