Later is a relatively flat company. UX Designers (UXD) is under the Product team.

Later UX Spec
Establish a consistent approach to design decisions
Overview
The UX specification (spec in short) is a document to record how UX decisions are made and to track & measure usability metrics. The process of documentation provides an opportunity for the designers to evaluate their decisions and create measurable UX goals that can validate their design via user testing.
Due to the growth of Later, having concise, proper documentation is an integral part of communication. This has become more important as we are now 100% remote as a result of COVID-19. The UX spec is aiming to provide clarity in UX decisions by stating the whys, the whats and the hows.
A little bit about Later teams
Later have grown from 20 to 100 staff in the past three years. Knowledge sharing has become an area of focus. We believe accessible information will ensure clarity in our communication, which is the main driver to collaborate better. This is why Later uses Slack, Notion and Google Suite Products to ensure the right people can access the right information.
The overall design and build process of a feature is based on the following team structure.

A little bit about the process
All feature specs are created in Notion by the Project Owners. They will work with
the CEO / Head of Product to outline the business goals that are driven by data. The spec will include user stories, acceptance criteria, links to related documents, customer feedback that support the business goals, and any additional relevant information. The primary goal is to ensure the whys, the whats, and the hows are clearly stated. This way we can get better team alignment.
The spec will be reviewed and discussed in a kick-off meeting and all key stakeholders from the four teams will participate. All discussions and decisions will be documented for reference. As more people are involved, the list of technical decisions and concerns has also grown.

Source: Lucidchart
Agile-Waterfall Hybrid
At Later, we adopt the Agile-Waterfall hybrid method. This methodology encourages an iterated approach to design and software development. Being nimble is one of the Later core values so the agile mindset is a perfect match.
Note: Later has added an agile component to the Document Requirements step. The goal is to collect insights from other teams that encourage collaboration earlier in the process.
Here comes the UX Spec
As mentioned, accessible information is an integral part of maintaining good communication. Good communication is the foundation of successful collaboration, especially in a remote environment. The UX team will need to share the design process in a concise document, which is the UX spec.
Aside from the stated benefits, I also see the UX spec as a platform to share the Later UX Principles (a high-level UX guideline that I have worked on with the CEO) with the rest of the teams. Using a shared set of UX principles will encourage team alignment in the early design process and advance Later's UX maturity as a company. Ultimately, the goal is to ensure Later delivers the best possible experience for our customers.
To summarize, there are four primary goals:
To increase UX principles’ visibility
To keep track of UX debts (decisions that compromise UX principles)
To help customers to develop useful behaviour that helps them maximize the use of Later (more on this later)
To track and measure usability metrics
Sneak Peek
I am unable to show the entire UX spec due to NDA. I can, however, share the general template and one section.
Each spec will have four sections:
Information Architecture
UX Principles
Octalysis Analysis*
Usability Plan
Under each section, there is a to-do list to help UX designers organize the necessary task in order to complete the section correctly.
* Octalysis Analysis is a framework developed by Yu-kai Chou. It is an excellent way to understand people motivation. It is a great tool to develop human centred design that influences your customers behaviour.

Each section will have a brief description to reiterate the purpose. There is a specific To-Do List corresponds to each section.
Make sure it flows
Each new feature will need to be considered in how it fits into current Later's information architecture. This is an important component of a good user flow.

Understanding Motivation
Ease of use is one of the UX metrics that Later measures. However, there is a lack of qualitative approach to define and determine what it is exactly. Leveraging the Octalysis framework and the BJ Fogg Behaviour model, the UX team is now equipped with a tool that can explain the ease of use in a consistent and concise manner.
Final Thoughts
The feedback from the UX team is that this is an excellent reference for the designer who recently joins the team. This document serves as a checklist for any required deliverables during the design process.
One of the new designers agrees that this is an ideal document for onboarding a new designer. Once the designer is more comfortable with the product and the process, this document will not be used as frequently.
After receiving this feedback, I have included the UX Spec as part of the onboarding documentation for future designers. This document, like others, is available on the UX Team’s Notion page for reference.