Bridge Letters and SOC Reports: A Practical Guide for Risk and Compliance

In today’s outsourcing-driven landscape, organizations increasingly rely on service providers for critical operations—from cloud hosting to payroll processing. To gain assurance over the controls at these providers, many engage with SOC reports prepared under the AICPA framework. Yet a SOC report reflects a fixed point in time, and business or regulatory needs often extend beyond that date. This is where a bridge letter enters the picture. A bridge letter is a concise, interim communication that helps bridge the gap between the SOC report’s coverage period and the current or upcoming operating period. This article explains what a bridge letter is, how it complements a SOC report, and how both buyers and providers can use this tool to strengthen risk management and vendor governance.

What is a SOC Report?

A SOC report, short for Service Organization Control report, is an independent examination of a service organization’s controls relevant to financial reporting (SOC 1) or overall security, availability, processing integrity, confidentiality, and privacy (SOC 2). A SOC 1 report focuses on controls at a service organization that could impact a user entity’s financial statements. SOC 2 reports evaluate a broader set of trust service criteria. SOC 3 is a public-facing summary of SOC 2 controls. The SOC examination is typically performed by an independent auditor and results in a detailed report describing the control environment, testing performed, and any agreed-upon changes or deficiencies as of the report date. While highly valuable, a SOC report covers a defined period and does not automatically address events that occur after its date.

What is a Bridge Letter?

A bridge letter is a short, formal letter from a service auditor or service organization that provides interim information between the SOC report date and a later period. It can confirm that there have been no changes to certain controls, describe changes that have occurred, or identify new risks and the steps being taken to address them. Bridge letters are commonly used when a user entity has a need to rely on controls for a period that extends beyond the SOC report, or when audit work on the client’s financial statements is ongoing and the SOC report cannot cover the most recent period.

Why Bridge Letters Matter

For many organizations, relying on a services provider is essential to operations, and decisions about vendor selections or renewals are time-sensitive. A bridge letter helps reduce residual risk by providing timely assurance about critical controls outside the SOC report’s window. It serves several purposes:

Clarifying whether core controls remain in place and operating effectively since the latest SOC report.
Disclosing changes to control environments, including newly implemented controls or material deviations.
Highlighting significant incidents or events that could impact control effectiveness and the provider’s remediation efforts.
Offering stakeholders a continuation path for due diligence activities without waiting for a new SOC engagement to conclude.

When is a Bridge Letter Used?

Bridge letters are most commonly requested in situations such as:

Client audits that overlap with the service provider’s reporting cycle, creating a need for assurance beyond the SOC report date.
Post-report events, including system upgrades, mergers, acquisitions, or incident responses, that could affect control effectiveness.
Contract renewals or procurement cycles where a SOC report is approaching its expiration, but ongoing assurance is required.
Regulatory or internal compliance programs requiring timely confirmation of controls while a new SOC engagement is underway.

Typical Contents of a Bridge Letter

Although the format can vary, most bridge letters include several common elements to maximize clarity and usefulness. A well-prepared bridge letter should address:

The period covered by the bridge letter and its relation to the SOC report.
Confirmation that the service organization’s control environment remains in place, or a description of any changes since the SOC report date.
A description of newly implemented controls or changes to existing controls, including implementation dates and responsible parties.
Any material deficiencies, exceptions, or remediation status that could impact the user entity’s risk posture.
Resulting impact on the user entity’s control reliance and suggested compensating controls, if applicable.
The date of the bridge letter, the authorized signature, and contact information for follow-up questions.

How to Read and Assess a Bridge Letter

Readers should approach a bridge letter with a critical eye, using it to complement, not replace, the SOC report. Helpful steps include:

Check the scope: Compare the bridge letter’s coverage against the SOC 1 or SOC 2 scope to ensure alignment with the services you rely on.
Evaluate changes: Distinguish between minor operational tweaks and substantial control changes. Understand the risk implications of each.
Look for exceptions: Note any material deviations or remediation timelines. Ask for evidence of remediation progress if needed.
Cross-reference with the SOC report: Use the bridge letter to bridge time gaps but not to override the conclusions or limitations stated in the SOC report.
Assess independent assurance: Determine whether the letter is issued by the same auditor who prepared the SOC report or by the service organization itself, and what that means for independence and credibility.

Risks and Limitations of Bridge Letters

Bridge letters can be valuable, but they come with caveats. Key risks and limitations include:

Not a substitute for a new SOC engagement: A bridge letter is interim and should be viewed as supplementary, not a replacement for a fresh SOC report when it becomes available.
Potential for partial disclosures: Letters may focus on selected controls or events, leaving other areas unchecked.
Dependence on provider honesty and rigor: The credibility of a bridge letter relies on the provider’s internal processes and the auditor’s independence.
Jurisdictional and regulatory nuances: Different industries may have specific requirements about what must be disclosed or how assurance is provided.

Best Practices for Buyers and Clients

Organizations seeking to minimize risk when relying on a bridge letter can adopt several best practices:

Define expectations up front: Request a bridge letter only after identifying the controls that matter to your risk assessment and determining the relevant scope.
Evince completeness: Ask for a concise map linking bridge letter content to the SOC report control objectives and testing results.
Mandate timeliness: Require the bridge letter to reflect events up to a clearly defined cutoff date and to be updated if major incidents occur.
Document acceptance criteria: Establish criteria for what constitutes acceptable residual risk and what constitutes a “no material impact” statement for certain controls.
Preserve procurement controls: Include bridge letter reviews as part of vendor risk assessments, due diligence questionnaires, and contract clauses.
Engage early with stakeholders: Involve internal auditors, information security, legal, and procurement teams to interpret the letter accurately.

Best Practices for Service Organizations

Service providers can improve the usefulness of bridge letters by adopting these practices:

Plan communications with care: Align bridge letters with major control changes, system upgrades, and incident responses to avoid surprises.
Maintain clear governance: Designate a single point of contact for bridge letter requests and ensure consistency with SOC report material.
Provide evidence-backed statements: Where possible, back bridge letter assertions with evidence, timelines, and remediation plans.
Ensure clarity and completeness: Use plain language to avoid ambiguity and explicitly state any limitations or caveats.
Coordinate with the SOC engagement: Share draft bridge letters with the same auditor when feasible to preserve independence and credibility.

Practical Scenarios and Examples

Here are a few real-world contexts where a bridge letter can play a pivotal role:

A cloud service provider releases a major platform upgrade after the SOC report date. The bridge letter outlines how the upgraded controls map to existing SOC criteria and notes any changes in testing scope.
An enterprise is preparing for year-end financial reporting while the service provider’s SOC 2 report is still in progress. The bridge letter confirms interim controls and remediation steps that impact the user entity’s control environment.
A merger or acquisition introduces new data flows with a service provider. The bridge letter highlights additional controls and risk mitigation measures implemented to address integration risks.

Conclusion

Bridge letters cannot replace the rigor and comfort of a fresh SOC report, but they offer a practical mechanism to maintain assurance during transitional periods. For buyers, a well-crafted bridge letter can reduce uncertainty, support timely decision-making, and strengthen vendor risk programs. For service organizations, providing clear, accurate, and timely bridge letters can build trust, differentiate offerings, and streamline client conversations. When used thoughtfully, bridge letters and SOC reports together form a robust framework for managing third-party risk in a dynamic business environment.